Many photonic circuits include interferometers or resonators, for example, to provide a periodic transmission spectrum for spectroscopy. Spectroscopy may, for example, be used for identifying molecules. Thereby vibrational information which is specific to the chemical bonds and to the symmetry of the molecules may be studied.
For spectrometer applications, the interferometer size may be small. Many of the typical interferometer components contain waveguide bends. These waveguide bends are introduced to create a path length difference between a first waveguide and a second waveguide of the interferometer. The presence of the waveguide bends can be very space consuming.
An example of such an interferometer is a Mach-Zehnder interferometer. Such an interferometer outputs a sinusoidal transmission as a function of wavelength. The sinusoidal transmission of a Mach-Zehnder interferometer is desired for many applications. The Mach-Zehnder interferometer itself is, however, is a very space-consuming device.
Another example of an interferometer is a ring resonator. Such a resonator gives Lorentzian shaped resonances. Ring resonators consume a lot of space in most material systems.
Yet another example interferometer is a Fabry-Perot resonator. The transmission spectrum of a Fabry-Perot resonator gives Lorentzian resonances. Fabry-Perot resonators can be made in a more compact form factor.
US2004/151436 discloses a scannable mirror arrangement for an interferometer. The interferometer in US2004/151436 comprises a scannable mirror moveable in an optical waveguide. The optical waveguide may be fluid filled and the mirror may be moved by an electromagnetic or electrostatic motor.
WO2012/015995 discloses a transform spectrometer measurement apparatus and a method for a planar waveguide circuit including phase shifting for error correction. The spectrometer typically includes an input optical signal waveguide carrying an input optical signal; a plurality of couplers, each connected to the input optical signal waveguide, and each including a coupler output for carrying a coupled optical signal related to the input optical signal; and an array of interleaved, waveguide Mach-Zender interferometers (MZI), each having at least one input MZI waveguide, each MZI input waveguide receiving a coupled optical signal from a respective coupler output.
Design parameters for an interferometer may include the size of the interferometer and the transmission, which may be predictable for different production runs. In view of the example interferometers described above, which either do not have a compact form factor or do not have a predictable sinusoidal transmission as a function of wavelength, there is still room for improved interferometers.